The present invention is directed to a device for controlling the opening of an ink fountain of a printing machine which device enables the dosing of the amount of ink to be supplied to the inking roller before the ink in transferred by the distributing rollers to the printing plate.
The quality of a printing run on offset printing machines depends on a number of parameters such as on the chemical characteristics and surface texture of the paper, the wettability of the plate of the plate cylinder, the printing speed as well as the quality and quantity of the printing ink delivered by the available inking system of the machine. Expressed with more precision, this means that the amount of ink carried onto the printing plate is to correspond to a minimum quantity required for insuring proper printing and as far as possible this minimum quantity is to be compensated laterally and longitudinally according to irregularities of the ink consumption which will correspond to the requirements of a given image.
The ink fountains of an offset printing machine consist in many cases of a very broad basin which has a sloping bottom wall that coacts with a rotating inking roller to form the entire basin. An opening of the ink fountain through which ink is supplied consists in a bottom slot or gap between the edge of the bottom wall and the surface of the inking roller and preferably a doctor blade forms this edge of the bottom wall. According to an early constructional concept, the doctor blade is applied in a fixed tangential position on the inking roller. Its outer longitudinal edge is then moved more or less towards the surface of the inking roller by the action of a number of equal distance setting screws. The major draw-back of this device is the impossibility of a fine adjustment at a given point without influencing the adjacent points. In practical application this design prevents accurate dosing of the quantity of ink to be supplied for printing a page which has strong vertical contrast.
With a view before limiting the interference appearing between the adjacent adjustment means, a suggestion has been made to subdivide the doctor blade into a row of lamellae or small plates which are arranged side by side in a plane and each of these plates have a separate mechanical or electro-mechanical means to shift the edge of the plate toward and away from the surface of the roller. A first example of such an arrangement is illustrated in U.S. Pat. No. 4,328,748 whose disclosure is incorporated by reference thereto. In this patent, every plate is normally pushed against the inking roller by a spring from which position it is pulled back by an electro-magnetic relay over a predetermined distance which is controlled by two stops. Considering only the possible "open" and "closed" positions of these lamellae, the quantity of ink flowing through the gap between the edge of each lamella and the roller is then determined by means of a time interval during which the various lamella remain in a retracted or open position. This device provides a "package-wise" inking delivery.
According to a second constructional concept, every lamella or plate acts as a short arm of a lever fitted in a rotary way along an axle close to the inking roll whereby the long vertical lever arm, that is turned downward, is shifted laterally by an intermediate piece within which a horizontal drive worm is actuated by an electric motor. In this assembly, a spring holds the long lever arm permanently against the intermediate piece. In this way, a double reduction effect is achieved first by means of a drive worm shifting the intermediate piece and secondly due to the dimensions of the respective lever arms and this enables the conversion of several revolutions of the electrical motor into a small displacement of the front surface or edge of each lamella. However, the relatively slow speed of the electric motor as well as the demultiplication do not allow a modification of the dosing action sufficiently quickly in cases with strong printing contrasts on pages with columns and line print. Moreover, it is impossible to avoid any mechanical precision inherent in the connection of the drive worm and the intermediate piece.
According to another constructional concept which is developed by the applicant, a setting piece is shifted in-line over infinitesimal distances owing to a screw with two different threads of which one is screwed into a frame and the other into an intermediate piece. This screw is driven by an synchronous AC motor through a reduction gear. Considering the minor or weak movements at the end of the reduction gearing, it is only possible to hold this device in position if a movement measurement is taken from the second demultiplied outlet motion of the reduction gear so that the measurement does not take into account possible mechanical clearances or play within the reduction gear or in the connection between the outlet shaft and the differential threaded screw at the level of the threads and the corresponding tapped orifices or bores. Moreover, there is no possibility to modify the speed of the synchronous motor if the motion of the setting piece is to be accelerated. Finally and especially this device represents a complex design involving considerable manufacturing expenses and maintenance costs.